1. Field of the Invention
The present invention relates to a signal processing device, and more particularly to a signal processing device which can be suitably applied to where a certain function is to be added to, to be removed from, or to be replaceably compensated for in it.
2. Description of the Related Art
Often a signal processing device requiring high speed signal processing has been realized by a wired logic circuit in which logic gates are connected by wirings. In order to implement conditions of small size, light weight, low power consumption and high speed, such a signal processing device has been integrated on a monolithic or plural LSIs with the aid of gate arrays, standard cells, full-custom. With development of semiconductor miniaturized-processing technology, the number of transistors which can be integrated on a monolithic LSI has been increased every year and an integration degree in signal processing device is getting increased. A new function can be added to the conventional signal processing device in such a manner that the signal extracted from the device is processed to provide the new function by e.g. another signal processing device and the processed signal is taken in the device again. However, because of the problems about power consumption, the number of input/output terminals of a package, the number of pads on a semiconductor chip, etc. generally, the high-integrated conventional signal processing device has a limited input/output means including an input terminal for inputting the signal to be processed, an output terminal for outputting the processed signal, a test terminal for failure diagnosis of the signal processing device, a power supply terminal and a ground terminal. Nevertheless, in order to add the new function to the signal processing device, as the case may be, the signal which cannot be inputted or outputted by the above limited input/output means must be inputted or outputted. Under such a circumstance, the conventional signal processing device cannot be used to add the new function to itself, but an individual signal processing device provided with a new function must be newly fabricated. Such a problem applies to not only to the above case where a new function is to be added, but also to the cases where a certain function is to be removed and where the function at a poor operation part due to erroneous circuit design and causes on semiconductor fabrication is to be replaceably compensated for.
There have been some proposals for providing flexibility in signal processing through software processing as disclosed in JP-A-1-255864, but no proposal for realizing flexibility in wired-logic structure.